However, I also think until kids properly learn the difference between inside and outside conversations/voices (I.E. I wouldn't have a loud conversation about my s3x life in public because no one else wants or needs to hear it and it isn't appropriate) that as adults it is up to us to explain the difference. So, if her DS was singing it quietly to other DS, then there's no problem. If the store member was deliberately eavesdropping and developed a problem with it, then I'd think she just needs to stfu and put her big girl panties on. If anewmes DS was singing it loudly enough for others to hear without a problem and deliberate eavesdropping then I think it is appropriate to ask her if he can sing a bit quieter so other people don't hear. But I don't think anger should ever be directed toward a child for what could be a learning thing, which is appropriate conversation levels in public as opposed to at home/in the car/in your own back yard.